1. Field of the Invention
The present invention relates to a hermetically sealed magnetic sensor for detecting variations in a magnetic field, more particularly, the present sensor is intended for use in an automobile etc., which requires an effective sealing against the external environment.
2. Description of the Prior Art
In general, various sensors such as a rotation sensor, a temperature sensor, a pressure sensor, an acceleration sensor and the like, are known for use in an automobile or the like. In particular, rust resistance against brine or the like, vibration resistance, shock resistance, water tightness and the like are required for a rotation sensor for detecting the wheel speed etc. mounted in a tire housing, for example, which is directly exposed to the external environment.
FIG. 1 is a sectional view showing an example of a conventional rotation sensor 1 having a sensor means including a magnet 2, a coil 3, a magnetic pole 4 and a bobbin 5 contained in a case 8. Terminals 6 are provided on both ends of a winding wound on the coil 3, to be connected to an end of an output wire 7. A resin member 9 is formed within the case 8 by resin molding. An output wire protective member 10 is provided around a part of the output wire 7 located in an opening of the case 8. Thus, the output wire 7 is convered by the resin member 9 through the output wire protective member 10 in the opening. A bracket 11 is mounted on the outer side of the case 8, to fix the rotation sensor 1 in a prescribed position.
The resin member 9 is generally made of thermosetting resin, such as epoxy resin.
In the conventional rotation sensor as hereinabove described, the resin is molded in the case to fix the sensor element in the case and the output wire connected thereto, as well as to maintain a water/air tight of hermetic seal of the case. However, such a conventional rotation sensor does not necessarily have a sufficient water/air tightness. A more reliable structure having a better water/air tightness is required particularly for a sensor for an automobile etc., which is used for a long time under severe operating conditions. Such a sensor for an automobile further requires an improved mechanical strength such shock resistance, since the same is subjected to extreme vibrations during operation of the vehicle.